This invention relates to air compressors, or like apparatus, and in particular to piston and cylinder assemblies for such apparatus.
In U.S. Pat. No. 4,275,999, which is assigned to the assignee of the present invention, there is disclosed an air compressor which employs a wobble piston with a unitary flanged filled Teflon disc or cup which serves both as a guide for the wobble piston and as a pneumatic seal of the piston to the wall of the cylinder in which it moves. The working surface of the cylinder has a hardened polished surface, providing a smooth surface for cooperating with the filled Teflon seal of the piston. A plate secures the seal to the piston for holding down the seal. The seal has a radially extending portion and an axially extending portion extending normal to each other, the outer surface of the axially extending portion engaging the polished inner wall of the cylinder and moving therealong as the piston is driven to provide the seal between the piston and the cylinder wall.
In this sealing arrangement, the sealing member moves generally tangential in providing a seal between the cylindrical piston and cylindrical wall. In time wear on the seal member will result in loss of seal, necessitating replacement of the seal. The lifetime of the sealing member is particularly reduced when employed with a wobble piston which exhibits rocking motion as well as reciprocating motion. In such application, sufficient clearance must be provided between the piston and the cylinder to allow rocking motion of the piston. The sealing member must continuously fill the space provided between the piston and the cylinder wall for maintaining a proper operation. Compression of the sealing member between the piston (or seal retainer) and the cylinder wall with rocking motion of the piston greater shortens the lifetime of the sealing member.
The piston contains a flexible intake valve through which the compression cylinder is loaded on the piston downstroke with a charge of air which is then trapped by the intake check valve on the upstroke of the piston. The compressor also includes a discharge check valve in its cylinder head which opens on the upstroke of the piston to receive the compressor delivery and closes on the piston downstroke to prevent backward flow from the discharge chamber into the cylinder.
The intake valve is in the form of a flexible thin spring metal planar closure strip which is stationarily fixed at one end but inclined at a small angle to the planar seat provided about the piston intake port. Such a valve closure strip is capable of flexing outwardly on the downstroke of the piston to admit a charge of air into its compression chamber and its snugly engages the valve seat on the compression stroke so that maximum quantity of the captured charge of air is delivered into the receiving chamber thereof.
However, the inclined valve seat allows the valve closure strip to come to rest at a position spaced off the surrounding valve seat each time that the compressor is halted. The uncovered intake port vents the compression chamber so that on startup there is an equalization of pressure inside and outside the cylinder. While such arrangement results in reduction in the torque requirement of the piston drive motor so that the compressor can be easily started and restarted, the requirement of a valved port in the piston makes for a complicated piston structure with an attendant high cost to manufacture.